Different types of tools are used to perform hundreds of processing operations during processing of wafers (i.e. semiconductor substrates) in wafer processing systems. Most of these operations are performed in vacuum chambers (i.e., process chambers) of a wafer processing system at very low pressure. Other operations are performed at atmospheric pressure in controlled environments of filtered air or an inert gas. Wafers are introduced to the process chambers with wafer transfer systems (i.e. wafer handling systems) that are mechanically coupled to respective process chambers such that a wafer transferred to the process chamber may be processed in the process chamber. Wafer transfer systems can include, for example, equipment front end modules (EFEMs) which are operable to transfer wafers from a front opening unified pod (FOUP) to the wafer processing system for processing and back to the FOUP, load locks to bring the wafers from atmospheric conditions to very low pressure conditions (e.g., vacuum conditions) and back to atmospheric conditions wherein robots transfer the wafers to various positions in the wafer processing system. Throughput (i.e., the number of wafers that are processed in a period of time) is affected by the wafer processing time as well as wafer transferring time.
When transferring semiconductor wafers via a robotic arm end effector, ensuring that the wafer is properly located on the end effector when first picked up, and also ensuring that the wafer does not slip or shift during the transfer and subsequent placement of the wafer on a support surface is required such that the wafer will not be damaged or misaligned during the transfer of the wafer. Additionally, repeated proper placement of wafers on a support surface of a processing module increases wafer processing throughput by eliminating the need to readjust a wafer which has not been properly placed on a support surface of a wafer processing module or improperly held by an end effector. Thus, there is a need for end effectors which can properly locate a wafer thereon when the end effector picks up a wafer, and end effectors which can properly place a wafer on a support surface such that the placed wafer does not need to be readjusted.